Conventionally, there is known a decoloring device that performs a decoloring process that heats a sheet, on which an image is printed by a decolorable coloring agent, to thereby decolor the image and puts the sheet in a reusable state. Even though decoloring is performed with respect to a sheet which is stapled, it may be difficult to reuse. Therefore, there are some decoloring devices, in which a thickness of the sheet is detected before the decoloring and whether or not the sheet is stapled is detected.
Most of the sheets on which the decoloring is performed by the decoloring device have a specific size. A user rarely decolors sheets having other sizes with a decoloring device, but the user does demand a decoloring device capable of decoloring sheets having other sizes.
However, when the device is configured such that the thickness is detected for sheets of every size before the decoloring and whether the sheet is stapled or not is detected, there are problems that the configuration of the device may be complex, and an increase in size and cost of the device may be generated.